Inverse emulsion polymerization is a process that produces high molecular weight, water-soluble polymer in a convenient package for application. In the process an aqueous monomer solution is emulsified within an inert hydrocarbon phase containing surfactants that promote water-in-oil (“w/o”) emulsions. The resulting droplets are polymerized yielding polymer particles that are dispersed throughout the hydrocarbon phase and stabilized by surfactant.
Over time various emulsification systems have been discovered and utilized. In U.S. Pat. No. 3,284,393, Vanderhoff and Wiley espouse the use of conventional w/o emulsifiers such as, sorbitan monooleate, sorbitan monostearate, hexadecyl sodium phthalate, cetyl or stearyl sodium phthalte, and metal soaps.
U.S. Pat. No. 3,826,771, to Anderson and Frisque, also teaches the use of conventional w/o emulsifiers, showing the use of sorbitan monostearate in all of the examples.
U.S. Pat. No. 4,024,097, to Slovinsky and Hurlock, introduced partially esterified lower N,N′-dialkanol substituted fatty amides, salts of fatty tertiary amines, quaternary salts of fatty tertiary amines, alkali metal salts, and alkyl or alkyl aryl sulfates and sulfonates as w/o emulsifiers that yielded lattices with smaller particle size distributions and improved storage stability.
In U.S. Pat. No. 4,147,681, to Lim et al., w/o emulsifiers with a HLB of at least 7 were used and many examples were cited. Lim and U.S. Pat. No. 4,672,090, to Chan, made use of a system comprising a polyoxyethylene derivative of a sorbitan ester, sorbitan monooleate, and alkanolamide.
In U.S. Pat. No. 4,906,701, to Clark, an inverse emulsion system utilizing polyoxyethylene sorbitol esters, polyoxyethylene fatty alcohols with a HLB of 7-9, and glycerides was revealed.
U.S. Pat. No. 5,206,316, to Chuang, revealed the use of nonionic oil-soluble surfactant and a compound selected from, N-alkyl lactams, and an alkylated polymer of a N-vinyl lactam.
With this in mind, it was desired to create an environmentally friendly oil phase system useful for making inverse emulsion polymers. The adopted definition of environmentally friendly are the rules that govern offshore chemical use in the North Sea. The environmental impact of a chemical is defined by three tests: bioaccumulation, biodegradation and toxicity. In order for a chemical to be used without restriction offshore in the North Sea it must satisfy two of the following three criteria:                1. Biodegradation must be greater than 60%, if less than 20% it is automatically marked for substitution.        2. Bioaccumulation as measured by octanol/water partitioning coefficient (log Po/w) must be below 3 (or have a molecular weight>700).        3. Toxicity to the most sensitive marine species (typically Skeletonema) must be greater than LC50 or EC50 of 10 ppm.        
One of the most popular and conventional w/o emulsifiers, sorbitan monooleate, does not pass the biodegradation and bioaccumulation protocols that govern offshore chemical use in the North Sea. For the initial assessment procedure, one must use marine biodegradation data as outlined in Organization for Economic Cooperation and Development, Procedure OECD 306 or BODIS. Sorbitan monooleate has a BODIS result of 32%, which coupled with log P>3 prevents sorbitan monooleate from passing the test. Other governing bodies allow the use of other types of biodegradation data such as the OECD 301 series (freshwater) to prove a chemical's non-harm to the environment, but not for use in offshore applications. This prompted an investigation into other w/o surfactant systems that could be used to produce inverse emulsion polymers.
Lecithin is well known as an emulsifier and has been used in w/o emulsion technology in explosives. A number of publications illustrate this application including U.S. Pat. Nos. 3,535,174; 4,308,081; 4,357,184; 4,473,418; 4,507,161; and 4,602,970. Of particular interest, U.S. Pat. Nos. 4,943,389 and 5,008,037 indicate that lecithin can be an inferior emulsifier for w/o emulsions. The patents teach that lecithin can be made into a better w/o emulsifier after subjection to a thermal process. Although inverse emulsions using lecithin are well known in the literature, not all inverse emulsions can go through the polymerization process and provide usable product.
Accordingly, there is a need for an environmentally friendly, oil phase system used for making water-in-oil emulsion polymers. Desirably, the oil phase system is biodegradable according to current environmental standards. More desirably, the oil phase system is comprised of substances recognized worldwide as generally safe for use.